1. Field of the Invention
Ultraviolet radiation sensitive photothermographic emulsions which are coated on both sides of a transparent carrier layer can be provided with good anti-crossover effects by selection of emulsion sensitivity and radiation absorption properties of the carrier layer.
2. Background of the Art
Radiographic images are traditionally formed on transparent substrates so that the images may be viewed by backside transmission lighting of the image. It is particularly advantageous to generate radiographic images within a cassette having X-ray intensifying (conversion) screens on each major interior surface of the cassette. Radiation sensitive film having a separate emulsion on each side of a transparent carrier film is used within the cassette. Each emulsion is sensitive to the emission wavelengths of the adjacent intensifying screen, with both screens usually emitting at or about the same wavelengths.
These systems are quite useful, but a significant problem is encountered in the use of the two-side coated film. Light from one screen that is not absorbed or attenuated by the adjacent emulsion will pass through the carrier layer possibly forming a latent image on the opposite emulsion layer. This image is referred to in the art as crossover. The problem with this image formed by crossover is that it is farther away from the emitting screen. As the emitted radiation is not moving exclusively perpendicular from the surface of the screen, the latent image formed by crossover radiation is of much lower resolution than the image formed in the adjacent emulsion layer.
In all imaging environments where two side coated imaging systems are used in cassettes, and especially in medical imaging and even more particularly in industrial radiographic imaging, this loss of resolution is undesirable. The traditional means of reducing crossover is to add dyes into or onto the transparent carrier layer, the dye absorbing the visible radiation emitted by the intensifying/converting screens. Such systems are shown in U.S. Pat. Nos. 4,803,150, 4,478,933, 4,425,426 and 4,500,631. EPO application Ser. No. 0 350 883 A2, published Jan. 17, 1990, disclosed the use of two screens with different emitting wavelengths and two emulsions, each emulsion being spectrally sensitive to only one of the emitting screens in order to reduce crossover.